The present invention relates to a method and to an apparatus for the non-destructive testing of spot welds.
The invention more particularly relates to a method making it possible to measure the diameter of welds and deduce therefrom the effectiveness of these welds.
Several non-destructive testing methods have been proposed for industrially controlling spot welds. These methods include the Fokker method and signature analysis by mechanical impedance.
The Fokker method which is used for controlling the cohesion of an adhesive joint between metal plates cannot be used for the inspection of spot welds. The reason is that the surface state of the welds is not identical between individual welds. As a result there are coupling variations between the structure of the welds and the piezoelectric transducer making it possible to carry out this method. These variations mask the variations due to the quality of the welds.
The second method, which is based on signature analysis by mechanical impedance has given better results than the aforementioned method. This method, which is very difficult to perform, uses a system of measurements and apparatuses for plotting a mechanical impedence diagram permits the overall testing of the soundness of all the welds in a metal member. However, it does not permit the individual control of welds or the determination of the diameter of each weld.